Ocean Drilling Program (ODP) Sites 1257–1261 recovered thick sections of Upper Cretaceous–Eocene oceanic sediments on Demerara Rise off the east coast of Surinam and French Guiana, South America.

Paleomagnetic and rock magnetic measurements of ~800 minicores established a high-resolution composite magnetostratigraphy spanning most of the Maastrichtian–Eocene.

Magnetic behavior during demagnetization varied among lithologies, but thermal demagnetization steps >200°C were generally successful in removing present-day normal polarity overprints and a downward overprint induced during the ODP coring process.

Characteristic remanent magnetizations and associated polarity interpretations were generally assigned to directions observed at 200°–400°C, and the associated polarity interpretations were partially based on whether the characteristic direction was aligned or apparently opposite to the low-temperature “north-directed” overprint.

Biostratigraphy and polarity patterns constrained assignment of polarity chrons. The composite sections have a complete polarity record of Chrons C18n (middle Eocene)–C34n (Late Cretaceous).